The present invention relates to systems for mounting plates, more specially offset lithographic plates with stretch properties, on the plate cylinder of a printing press. In the prior art such a system may be made up of a well running along the length direction of the cylinder and having clamping members placed on its two sides, each of such clamping members having its own gripping part for gripping the hooked ends of the printing plate, and at least one of the clamping members is able to be rocked about an axis parallel to the axis of turning of the cylinder in the printing press.
A system designed on these lines is for example to be seen in the German Pat. No. 2,759,434. In this known system the rocking clamping member is in the form of a rocking flap of L-like cross-section which was able to be rocked about an axis at the side of the well. Using the rocking flap the hooked edge part of the plate was pulled into the well over the edge thereof. A shortcoming of such known systems was the fact that the well had to be made quite broad in the round-the-cylinder direction so that a large part of the cylinder would necessarily not have any printing plate, and for this reason any printing image thereon so that the press would be less economic to run. A further point to consider was that the plate was likely to be bent on being put on and taken off the cylinder so that it would then be damaged and useless for further printing. A still further shortcoming was that the rocking mounting flap was not able to be locked in place and was only acted upon by a stack of springs moving it into the plate-fastening position. Such springs might then be caused to vibrate in operation and the plate would then no longer be firmly seated on the plate cylinder.